small chip in grout line

Just had tile layed in the kitchen floor. Sealed teh grout lines with spray sealer and it worked very well. After I was done and inspecting everything I noticed there was a small chip in the grout and it is white and the grout lines are a lighter grey. Can I make a small bit of the grout and patch it? it is only 1/8 in. round. I am sure he used the grey thinset to lay the tiles. Any other suggestions. The floor does look very nice.
Thanks,